A major problem in semiconductor devices is protection of the bonding areas and underlying devices from the environment. The surface of devices, in the past, has been protected by oxide layers in which windows are formed to make contact to the underlying bonding pads. The complete devices usually are then sealed in a ceramic or metal housing, or given only mechanical protection by enclosing in a molded plastic package. These housings add bulk to the devices, increasing the sizes of electrical wiring assemblies and, of course, add the expense of providing such ceramic, plastic or metal housing.
To eliminate the necessity for a hermetically sealed housing, it has been proposed to seal or cocoon semiconductor devices of the type including aluminum bonding pads by applying a barrier layer to the bonding pad, followed by a layer of gold to which a gold wire lead is bonded. The barrier layer prevents the diffusion of the gold into the aluminum bonding pad. A layer of silicon dioxide is then applied to the semiconductor device, including the bonding wire. In certain instances another layer of silicon carbide titanium nitride or other layers are formed over the silicon dioxide. A major problem encountered with this technique is that cracks occur at the wire-to-gold bond layer interface with thermal changes, and thereby allow ingress of moisture, harmful gases and other contamination of the underlying semiconductor material. Furthermore, the silicon dioxide layer alone is not impermeable to certain ions which penetrate through the layer and damage the underlying devices.